The present invention relates to an emulsion polymerization process for the preparation of grafted and occluded rubbery particles. More particularly, the present invention relates to such an emulsion process allowing great flexibility in the preparation of rubbery particles having a relatively large volume of occluded matrix polymer.
The preparation of rubbery graft copolymers by emulsion techniques is well known in the art. Suitably, a preformed emulsion of a rubbery polymer such as a homopolymer or copolymer of a conjugated diene is contacted with at least one suitable addition polymerizable monomer and the resulting mixture subjected to polymerization conditions. Suitably a free radical initiator such as the well known peroxide initiators is included and the mixture is exposed to elevated temperatures until substantially complete polymerization of the monomers is achieved. The latex is recovered and dewatered by well known techniques to achieve a solid thermoplastic polymer. The resulting polymer normally contains a matrix of the polymerized monomer or monomers and dispersed therein rubbery particles having grafted thereto and occluded therein additional quantities of the matrix polymer. Such emulsion polymerized polymers are suitably employed as thermoplastic molding resins and depending on the monomer or monomers employed have found wide spread use.
The efficient utilization of rubber particles in imparting impact resistance to thermoplastic resins requires that the phase volume of such rubber particle should be maximized. Generally, by increasing the rubber phase volume greater impact properties of the resulting thermoplastic resin are obtained per unit weight of rubber employed. The modulus, however, generally decreases as the percent of rubber is increased. One suitable technique for increasing the phase volume of rubber particles involves preparation of such rubbery particles containing therein occlusions most generally of the hard matrix polymer sought to be impact modified by the rubbery polymer. This technique does not decrease the modulus significantly. Because of the polymerization conditions employed in the emulsion polymerization of impact modified thermoplastic resins, it is not possible to attain rubbery particles containing large amounts of occluded matrix polymer. Normally effective monomer migration and partitioning into the rubbery phase is not possible utilizing standard emulsion polymerization conditions and, therefore, such conditions are not suitably adapted to the preparation of rubbery particles having improved rubber phase volume.
It would be desirable if there were provided an emulsion polymerization process for preparing grafted and occluded rubbery polymers, wherein the rubbery particles contain an improved quantity and size of occluded matrix polymer thereby resulting in an improved rubber phase volume, without substantial loss in modulus.
In addition, it would be desirable if there were provided an improved polymerization process for preparing impact modified thermoplastic resins containing the above improved rubbery particles.
In addition, it would be desirable if there were a product having both a high level of occlusions and the uniformly near spherical geometry produced by emulsion polymerization. Particularly desirable is the relatively transparent product which is obtained when the occlusions are relatively small (below about 700 Angstroms) and/or constitute a larger portion of the rubber particle.